77 f-150 4x4. brakes have been spongy since I've owned the previous owner told me. they work for now and i thought it would be a good winter project.

i replaced the front brake cailipers,front and rear pads, rear drum hardware, fount brake lines to braided s.s. steel. power stop rotors, master cilyender. still pedal feels spongy and can't get the air out of the rear brakes.

looked for leaks found one! at the brake warning switch on the porportion valve.replaced the switch and it still leaks. so i replaced the proportion valve itself, no leaks.

since then i have LOST all pedal pressure, unless pumped 4-5 times. without the motor running. leave the pedal alone for 15-30 seconds, no pressure at all. with the motor running it takes about 10-13 pumps to get good pedal pressure. and i lose pedel if i leave the pedel alone. if i keep pressure on it just half or less i don't lose the pressure. i hear a squish sound from the booster and master cilyinder area, and i have noticed the steering calom moves when the brake pedel is pressed.

i have replaced so much stuff I'm not sure what could be left or if i skipped a step some were, master cilyder bench bleed, no air in the system that i have seen. ran about three bottles of brake fulid (abs dot 3). had two other friends bleed the brakes with me and look for leaks. nothing

i give up !! i would settle for the spongy brakes back instead of no brakes at all unless pumped.
i did use the spellcheck.net thank you for any help

 

A. You have air in the system, and spongy brakes may be caused by the master cylinder.

B. The old (new?) master cylinder may have leaked into the booster, that may be the squishy sound you are hearing.

These symptoms are not uncommon.

 

Also Pull the MC off the booster and check the back of the MC for a leaking seal.

Just because it is NEW doesn't mean it is GOOD.

One guy on here went thru 5 M/C's before he got a good one.
Make sure you get one with a stainless steel sleeve and not a Cast sleeve.

Also do a Brake booster check.

 

i will do that thank you for the tips...the repair book im useing dont tell me what the rod length coming out of the brake booster to m/c is does any one know?

 

Left side of page .

http://www.clubfte.com/users/mil1ion...trations2.html

 

ok i have spent the whole day checking these items with no luck..had two different friends check my work and they were unable to see any thing wrong. no air in system, no leaks. one of my pals even removed the tires, m/c, checked the booster bendix, bleed the lines. used 2 more bottles of fulid, with no improvement. they said something about "power flushing" the brake lines. i dont think it would help due to no air seen in the bleeding process. but im running out of choices.

 

Replace the brake vacum booster. I have a '77, it had the same problem.

 

Don't let these types of problems get you too frustrated, because then it gets hard to think logically. It still comes down to basics; brake fluid doesn't compress and air does. If you don't have any fluid leaks, the rear wheel cylinders are adjusted properly and the pedal still requires pumping, then you have air in the system somewhere.

Start with the master cylinder. Is it a new unit? Master cylinders can have a tendancy to leak fluid into the booster making you think they are OK even though they aren't, boosters can hold a LOT of fluid and every time you start the truck it sucks the fluid into the motor so you never really see the leak. Make sure the rear wheel cylinders are adjusted properly. If they are a little loose, they can be the biggest culprit of the problem you're describing.

If you've replaced a lot of the components, it can be difficult to get all the air out. I like to gravity bleed the system, just crack the bleeder screw without pumping the pedal and let the fluid dribble out to catch the final few air bubbles (a rubber hose over the bleeder screw going into a bottle makes this less messy). You shouldn't be going through whole bottles of brake fluid at this point in the project, just small amounts as you finalize.

Mainly just go to the basics of making sure all of your components are working properly, your problem will be something relatively simple.

 

the booster appears to be fine i think. im not sure or fully understand how the booster could suck fulid when i dont see loss of fulid in the m/c.
all tho i have seen very tiny bubbles in the drivers side rear wheel a few times but not every time. thats why my pals said to power flush the system but no one could tell me were to have this service done at. i have found the tool at summit for $100 bucks.
the booster is the last component that i have'nt replaced. and two rubber lines running from the hard lines off the frame to the axles.
would the e-brake not working at all have something to do with it? the cables need to be repalced.
i fully agree with everyone im over looking something. and i will say duh thats it!!

 

The master cylinder can leak brake fluid out of the back where it bolts to the booster. The booster is connected to the intake manifold to get the vacuum it needs to operate, thus the fluid can leak into the booster and be inhaled by the motor and you'll never see the leak. The booster itself it big enough that it can hold a lot of fluid even with no vacuum, probably a quart or two. A small leak can cause these problems, usually it will only be apparent if you see fluid leaking out of the back of the MC when you unbolt it from the booster, and the fluid loss can be so small that it'll take weeks before you notice the fluid level dropping.

Before you go through all that, I wouldn't worry about the power flushing, I've done numerous brake jobs on these trucks and never used anything like that, I just finished up a 78 Bronco 2 weeks ago that my 16 year old son is driving. I'd look into the rear wheel cylinders first to make sure they're adjusted properly -- jack up the rear wheels and adjust them out until the wheel is hard to spin, then back off a small amount.

Another basic although stupid thing that happened to me is after we finished replacing almost everything on the Bronco and couldn't get a firm pedal was that I was under the truck and noticed fluid dripping from one of the brand new fittings on one of the hose/lines we just put on a few days prior, and when I checked it, it was ridiculously loose -- something we just overlooked, but it was letting air into the system.

 

Try bleeding the master cylinder where the two lines connect to it. Have someone pump up the brake pedal with engine off and keep pressure on the pedal. Crack open rear line on the mc until the pedal goes down and tighten it back up. Pump up again and do this on each of the two lines until no air comes out. I aways do that when replacing and mc. Worked fine on my '77 F250 after bench bleeding, before and after bleeding at the wheels.

 

^
I'm with this guy. I would try that first.
Also start bleeding from the farthest wheel cylinder first (Rear passenger side then rear drivers side) and then work foward. I went through this and had to bleed the rear passenger side a dozen times before I got any air bubbles out.

What DOT brake fluid are you using?

Hang in there, You'll get it.

 

thank you guys it was a hard job, but without everyones tips i may have taken it to a shop !!
i was not getting air from any kind of bleeding the system. so i went back to the basics and checked from back to front and found the problem. the push rod from the brake booster did have fulid on the seal (from old m/c) i replaced the booster and still had the same problem. went over the install steps of the booster and found out the push rod was out of adjustment (not pushing far enough) after a few trys got them to work !!